When completing a well, production zones are provided by submerging a casing string having annular barriers into a borehole or a casing of the well. When the casing string is in the right position in the borehole, the annular barriers are expanded or inflated. The annular barriers are in some completions expanded by pressurised fluid, which requires a certain amount of additional energy.
In other completions, a compound inside the annular barrier is heated so that the compound becomes gaseous, hence increasing its volume and thus expanding the expandable sleeve. However, the diameter of a borehole or a casing may vary, and when the sleeve is expanded, the sleeve may damage the formation or collapse the casing if the diameter of the borehole is smaller than expected, i.e. an excess of expansion energy occurs. Furthermore, the sleeve of the known annular barriers may also fracture if the expansion energy is higher than required.